SSH fallback to local account if Radius server isn't available

Enable common-auth (includes pam_unix.so), and change "required" to "sufficient".

auth    sufficient      pam_radius_auth.so
@include common-auth

(2016/05/03 JST) settings for "fallback"

auth    [success=done default=bad authinfo_unavail=bad ignore=ignore]  pam_radius_auth.so localifdown
@include common-auth

Results of pam_radius_auth in the following respective cases:

                       | correct password (in Radius)         | wrong (or UNIX) password
-----------------------+--------------------------------------+-------------------------
Radius Server is alive | PAM_SUCCESS                          | PAM_AUTHINFO_UNAVAIL
-----------------------+--------------------------------------+-------------------------
Radius Server is dead  |             PAM_IGNORE (with localifdown option)
-----------------------+--------------------------------------+-------------------------

As a result:

PAM_SUCCESS          => done (Login success)
PAM_AUTHINFO_UNAVAIL => bad (Login failure)
PAM_IGNORE           => ignore (continue to "common-auth")

There is a note. If the time-out value in pam_radius_auth.conf is too small, it will determine "Radius Server is dead", before receiving the "Access Reject" from the Radius Server.